The invention herein is concerned primarily with the sealing of the doors of domestic cooking ovens and more specifically to a novel gasket for effecting such sealing.
The invention herein is an improvement over the structures which are disclosed in U.S. Pat. Nos. 3,029,805, 3,404,675, 3,765,400, and 3,810,483. The first of these patents, U.S. Pat. No. 3,029,805, proposed a gasket in the form of an elongate elastomeric member of tubular form having a strip of metal disposed on the interior thereof along the entire length, with protruding offset end tabs adapted to engage in slits formed in the front plane wall of an oven around the oven door opening thereof. The gaskets were supposed to be removable, but problems arose in manipulating these gaskets. The metal strip had to be flexed or bent in the process, as a result of which the gasket was distorted, and often loosened in place thereby weakening the seal. Since the gasket had to be manipulated by the housewife for cleaning, one could not expect that the mechanical dexterity required to assure proper bending and proper flexing would be had by such person.
The second of these patents, U.S. Pat. No. 3,404,675, proposed the use of a short metal insert at each end of the tubular member with an offset tab also adapted to enter slots provided in the oven wall. Since the member was intended to be made from an elastomeric material and hence be stretchable, it could be made slightly shorter than the distance between the slots so that it could be stretched and installed and remain tightly in position under some tension. Removing the gasket for enabling cleaning of the oven surface or to replace the same was also a simple process of stretching the gasket enough to relieve the tension on the tabs and removing the tabs from their slots.
The problem raised by the structure of said U.S. Pat. No. 3,404,675 is how to prevent the short metal inserts from being pulled out of the ends of the tubular gaskets when the gasket is placed in tension. The patent proposes the use of barbs formed on the inserts, facing in such a direction that the insertion of the metal member is readily accomplished, but any attempt to pull the insert out of the ends of the gasket results in the barb points biting into the interior walls of the gasket. This resisted removal.
From a practical standpoint, the conditions needed to achieve the operation described are difficult to meet, if not impossible to achieve. In order to dig into the elastomeric material sufficiently to resist withdrawal, the barbs have to enter so deeply that they protrude from the exterior of the gasket. Likelihood of tearing is present. Shallow barbs will not hold.
The fourth and fifth patents, U.S. Pat. Nos. 3,765,400 and 3,810,483, ostensibly solved the problems by eliminating the need for the barbs. Thus, these patents proposed the use of a metal insert engaged into each open end of the tubular member, which ends were held in place by means of a room temperature vulcanizable adhesive (RTV). The protruding ends of the metal insert had a hook-like configuration adapted to be engaged in suitable perforations formed in the front of the oven wall. Additionally, to assist the adhesive in its holding action, the portion of the metal insert positioned within the open end of the tubular member had through passageways to enhance the bonding of the adhesive within the interior of the tubular member. The gasket was made by dipping the insert portions of the insert into a container of the room temperature vulcanizing adhesive, inserting the same into the ends of the length of the tubular member, and subjecting the resulting assembly to steam for several hours, preferably in an autoclave. This cured the adhesive in moist conditions and was said to form an excellent bond.
Seals for the doors of domestic cooking ovens during the course of their use are subjected to relatively high temperatures, e.g. on the order of 400.degree. to 500.degree. during normal baking operations, and substantially higher temperatures when the oven is one of the self-cleaning types wherein the temperature of the oven is raised to a temperature high enough to substantially burn off the food particles and fats which tend to adhere to the walls of the oven itself.
To resist these elevated temperatures, the elastomeric material is usually a silicon type rubber. RTV's do not adhere well to such rubbers.
Additionally, in practice, it was found that the RTV adhesive disintegrated when repeatedly subjected to these elevated temperatures, with the result that after a relatively short period of time, the insert pulled out of the end of the tubular member, making the gasket entirely unusable.
Thus, the problem of fastening the metal hook to the ends of the rubber sealing portion of a gasket has been a continuing one through the years, and considerable effort, money, and research time has been expended to ultimately solve the problem.
It will be further noted that all such prior art gaskets employed a hollow tube of extruded elastomeric material which for a given sealing action has a much larger cross-sectional area of the expensive elastomeric material than is possible if the gasket were of a solid construction.